The Jasons are a group of remote islands, to the far north-west of West Falkland. Some are scenically spectacular, with cliffs and craggy peaks, while others are low lying and covered with Tussac. Steeple Jason is a large island, 5 miles (8 km) long, running south-east to north-west with an average width of around 0.6 miles (1 km). The island is divided into two main sections by a narrow neck, which marks the only break in a ridge of hills with steep slopes on both sides. The island peaks at 263 m towards the north and again at 290 m towards the south. At the northern point a wide, low plateau forms an important area for breeding colonial seabirds, which extend, in more scattered colonies, along the southern steep coastlines. The main stands of Tussac are along the southern shorelines and extend from around 30 m to the highest points of the island. Scattered patches of Tussac also exist in the centre of the island and there is a large stand in the middle of the northern half on the eastern coast. Grand Jason is the largest of the group and has a similar history of stocking to Steeple Jason. The terrain varies from steep cliffs and high plateaux with gullies to Tussac-covered west-facing and south-facing slopes. There are severely eroded areas of ‘black ground’, particularly at the northern, south-eastern and western extremities. The island’s peak is at 361 m and Tussac is sparse above 60–90 m, with low grasses and small cushion plants. Steeple Islet is a small island, generally low lying, with boulder beaches and low cliffs, sloping towards a rocky north-western point. Almost the entire island is covered in dense Tussac grass, which has apparently never been grazed. Flat Jason is a low-lying Tussac island with vertically dipping rock strata, and is possibly the largest island in the Falklands archipelago that has not been grazed, partly due to the difficulties of access. The island is almost 3.7 miles (6 km) long on a north-west to south-east axis, with an average width of some 600 m. At the centre of the island there is a narrow neck with a boulder beach that may sometimes be tidally inundated. The northern coasts are mainly boulder beaches with rocky outcrops, while the southern shores are more formidable, with steep-sided mini stacks and cliffs. Elephant Jason has a long ridge rising to a height of 208 m, sloping into low-lying plateaux thickly covered with dense Tussac on the northern and eastern coasts, and with sheer cliffs on the western coast. The fringe of Tussac extends around most of the island, giving way at the northernmost point to areas of grass and heath. For a short time early in the 20th century Elephant Jason was used as a base for government sealing inspectors, who constructed a shanty on the island. The remains of the cast iron stove can still be seen. South Jason is a long, narrow island, running almost due east–west and reaching over 4.3 miles (7 km) in length and only 0.6 miles (1 km) wide at its widest point. The entire island has a central ridge reaching around 300 m in height, flattening out to the east and west. The eastern point has a dense cover of Tussac, while the western point is drier, with sparse grassland and a small pond. The southern slopes are mostly covered with dense Tussac while the northern slopes are rocky, and the vegetation consists of dry upland heath, with Balsam-bog Bolax gummifera and exposed rock layers. South Fur is a small island lying around 3 miles (5 km) off the south coast of Steeple Jason. Just 0.6 miles (1 km) long and 300 m wide, its highest point is only 18 m. Unusually, it is composed mainly of large blue-grey dolerite boulders, with a dense but low Tussac covering. It has not been stocked with sheep or cattle. North Fur lies north-east of Flat Jason and is difficult to access due to steep cliffs formed from vertically bedded rocks. It is heavily overgrown with dense and tall Tussac, and has small amounts of Wild Celery Apium australe, Stonecrop Crassula moschata and Swordgrass Carex trifida, but it has never been stocked, probably because access is difficult. ‘Clarke’s Islet’ lies about 0.3 miles (0.5 km) off the north-eastern coast of Grand Jason. It is a rugged low island with many rock outcrops, patches of ‘black ground’ and open low Tussac, heavily used by Southern Sea Lions. The Fridays are two small islands situated around 3 miles (5 km) from the north-west coast of Flat Jason. Both are low lying, and consist of large coastal rocky strike ridges with Tussac between. On the larger of the two, this area gives way in the centre to open peaty ground, which is the site of a colony of Southern Giant Petrels. Southern Sea Lions use both islands.
On Steeple Jason in October and November 1997, 36 species were noted, with 27 probably breeding, and 39 species were recorded on Grand Jason with 30 of them almost certainly breeding. A total of 12 species, 11 probably breeding, were found on Steeple Islet during a visit of only 90 minutes. Clarke’s Islet held only 10 species, almost all breeding and including Cobb’s Wrens, Tussacbirds and Canary-winged/Black-throated Finches. On Flat Jason, 32 species were seen, with 26 probably breeding. On Elephant Jason, 33 species were noted, of which 30 were probably breeding. Populations of Thin-billed Prions, Wilson’s Storm-petrels, Grey-backed Storm-petrels, Rock Shags and Imperial Shags warrant further investigation. Endemic sub-species present are the Common Diving-petrel, Black-crowned Night-heron, Upland Goose, Short-eared Owl, Dark-faced Ground-tyrant, Falkland Grass Wren, Falkland Thrush and the Long-tailed Meadowlark. The Falkland Pipit is apparently absent from all islands in this extreme western group.
Non-bird biodiversity: The presence of breeding Southern Elephant Seal, Southern Sea Lion and South American Fur Seal has been confirmed on most of the islands in the group. About 200 Southern Sea Lion pups are born annually in the archipelago and there are many non-breeding adults and sub-adults. Islands Criteria Key species Number of Notes breeding pairs (if known) A1, A4ii Black-browed Albatross 213,800 Largest Falkland colony is on Steeple Jason Thalassarche melanophrys A1, A4ii Gentoo Penguin 12,300 Steeple and Grand Jason only Pygoscelis papua A1, A4ii Rockhopper Penguin 142,000 Steeple, Grand and Elephant Jason only Eudyptes chrysocome A1, A4ii Southern Giant-petrel 1,500 Main colonies on Grand and Steeple Jason, small Macronectes giganteus colony on The Fridays A1 Magellanic Penguin Numerous Breeding on Grand, Steeple, Flat and Elephant Spheniscus magellanicus Jason and North Fur, no counts A1 Macaroni Penguin 10 Maximum count Eudyptes chrysolophus A1, A2, A4ii Striated Caracara 250 Jason Group are the Falkland stronghold of this Phalcoboenus australis species A1, A2 Cobb’s Wren Numerous All islands except Steeple Jason Troglodytes cobbi A2 Ruddy-headed Goose 10 Few pairs on Grand and Steeple Jason only Chloephaga rubidiceps A2 Canary-winged/Black-throated Finch On all islands in group, not counted Melanodera melanodera A2 Falkland Steamer Duck All islands except Clarke’s, not counted Tachyeres brachypterus A2 Tussacbird/Blackish Cinclodes All islands in group, not counted but numerous Cinclodes antarcticus A4iii Combined seabirds >369,850 Key species 123 where breeding occurs are Steeple Jason (46 pups), Fridays (29), Flat Jason (17), Elephant Jason (26), South Jason (5) and South Fur (4). South American Fur Seals breed on Jason West Cay (2,000) and East Cay (2,000), Seal Rocks (200), Elephant Jason (200) and North Fur (33 pups). At least 43 flowering plant species occur including six endemics: Coastal Nassauvia Nassauvia gaudichaudii, Vanilla Daisy Leucheria suaveolens, Lady’s Slipper Calceolari fothergillii, Woolly Falkland Ragwort Senecio littoralis, Smooth Falkland Ragwort Senecio vaginatus and Falkland Rockcress Phlebolobium maclovianum. The most surprising plant found on Grand Jason was an unidentified purslane (Calandrinia), possibly a new endemic plant.
BirdLife International (2019) Important Bird Areas factsheet: Jason Islands Group. Downloaded from http://www.birdlife.org on 20/06/2019.